In one embodiment, the present invention discloses a series of nanoporous polyurethane-acrylate (PUAC) type materials for applications in structural insulation, thermal insulation, and the like. In another embodiment, the present invention discloses a series of urethane-acrylate (UAC) Star monomers, which are monomeric precursors for the preparation of the PUAC materials. In yet another embodiment, the present invention discloses one or more processes for the conversion of the UACs to their corresponding PUACs. In yet another embodiment, the present invention discloses methods of use of the PUACs as aerogel materials for applications in structural insulation, thermal insulation, and the like.
Aerogels have been known as three-dimensional lightweight porous materials formed by aggregation of nanoparticles, wherein the thickness dimension may vary greatly (from nanometers to meters) such that in some cases they may be viewed as quasi-two-dimensional objects. High surface areas and open porosities have been reported as being two of the most attractive properties for applications in thermal insulation, drug delivery, catalysis, and other applications. Aerogels are believed to have been first reported in 1931 by Kistler, who is believed to have introduced supercritical fluid (SCF) drying as a means to retain the network morphology of wet-gels into the final dry objects. Most post-Kistler attention appears to have focused on silica aerogels. Organic aerogels seem to have started getting attention after the synthesis of resorcinol-formaldehyde (RF) aerogels.
For a number of years, polymer- and RF-aerogels were almost synonymous terms. In the last few years, however, research on other polymer-based aerogels seems to have gained significant momentum. It is believed that the reasons include well-defined chemistry, molecular design flexibility, readily available raw materials, and the excellent mechanical, thermal, chemical, and other properties of these polymers.
In another embodiment, described herein are polymer aerogels obtained by using polyurethane-acrylate (PUAC) chemistry. PUAC polymers have been popular in the automotive and coating industries. It is believed that this is so because PUAC polymers incorporate properties of both polyurethanes and polyacrylates, and because they can be prepared easily by free-radical polymerization using UV light or heat. It has been observed that low density PUAC aerogels tend to be flexible, while higher density PUAC aerogels tend to possess greater stiffness and stronger mechanical properties.
It has been reported that flexible aerogels are interesting for a plethora of applications, illustratively, in planetary descent and landing (EDL) systems, thermal insulation, such as in sub-sea oil pipes (e.g., see http://www.aerogel.com/markets/subsea.html) and buildings (e.g., acoustic insulation), where flexibility and foldability are considered to be necessary properties. It has also been reported that the impressive strength-to-weight ratio of higher-density PUAC aerogels renders them attractive as energy absorbers for defense applications.
In another embodiment of the invention herein, thermally stable PUAC aerogels are described. In one aspect, the thermal stability of these PUAC aerogels can be as high as 300° C. In another aspect, the thermally stable PUAC aerogels are synthesized from inexpensive isocyanates and hydroxyl functionalized acrylates.
In another embodiment of the invention, described herein are polyurethane and polycarbonate aerogels, which are synthesized from urethane-acrylate or carbonate-acrylate star monomers. In one aspect, these star monomers are stable and easy to handle, as compared to highly-reactive isocyanates or phosgene. In another aspect, the raw materials used herein are inexpensive and readily available.
In another embodiment of the invention, described herein are inexpensive, multifunctional, light-weight, bendable nanoporous materials with high degree of flexibility. In one aspect, these materials may be prepared via easy, one-step synthesis methods, as will become apparent from the following discussion.
In another embodiment, as contemplated herein, the materials described in this invention may be useful as multifunctional thermal and acoustic insulating materials for buildings, sub-sea oil pipes, automobiles and aircraft, and as energy absorbers for anti-ballistic applications, such as, illustratively, armor and blast wave mitigation against improvised explosive devices (IEDs).
In another illustrative embodiment of the invention, the UAC Star monomers are compounds of the formula (I):
wherein the nitrogen atoms of the urethane moieties are independently attached to their respective aryl rings at the 2, 3, or 4-positions of the aryl rings; wherein each of W, X, and Y independently represents a C1-C6 straight chain alkyl group or a C1-C6 branched alkyl group; and wherein each of R1-R9 independently represents an H, a C1-C6 straight chain alkyl group or a C1-C6 branched alkyl group. It is understood that other related variations on the illustrative UAC Star monomers of formula (I) are contemplated herein, as will become apparent in the detailed discussion below.
In another illustrative embodiment of the invention, the PUAC polymers are compounds of the formula (II):
wherein the nitrogen atoms of the urethane moieties are independently attached to their respective aryl rings at the 2, 3, or 4-positions of the aryl rings; wherein each of W, X, and Y independently represents a C1-C6 straight chain alkyl group or a C1-C6 branched alkyl group; and wherein each of R1-R9 independently represents an H, a C1-C6 straight chain alkyl group or a C1-C6 branched alkyl group; and wherein n is an integer ranging upwardly from 2 upwardly to 100, 200, 500 or even higher. It is understood that other related variations on the illustrative PUAC polymers of formula (II) are contemplated herein, as will become apparent in the detailed discussion below.
In another embodiment of the invention, processes are described herein for the conversion of the UAC Star monomers to the PUAC aerogel polymers of the invention, as will be further described in the following discussion.